The objective of the research is to elucidate the participation of certain metabolically significant chemicals in the mechanisms which mediate local regulation of blood flow. The literature suggests that the most likely chemical candidates for such a role are O2, K ion, H ion and adenosine or its mononucleotides. During the next fiscal year, we plan to continue examining the roles of adenosine and the adenine nucleotides in active and reactive hyperemia in the coronary circulation. In addition, we will investigate the possibility that cardiac hypoxia releases adenosine from cardiac muscle. Finally, further studies will be performed to deliniate the role of prostaglandins in the regulation of renal blood flow.